The present invention relates to crimping dies and the like, and in particular to a crimping die that utilizes a powered chuck and segmented die to release a formed part.
Various types of metal forming dies have been used in the fabrication of a wide array of parts. One example is an electrochemical battery cell having a two piece cladding that is crimped together to form the finished battery cell. Known crimping methods utilize a one piece female die. A punch drives the two pieces of the cell into the female die segment, thereby deforming the outer edge of one of the cell pieces, and crimping the two sections together to form the electrochemical cell.
One problem encountered in such an arrangement is that the formed steel part will have some residual stress, causing the part to "spring" outwardly against the inner sidewalls of the female die segment. The friction generated between the part and the sidewalls of the female die segment can make removal of the formed cell difficult, leading to damage of the cell. Although lubricants may aid removal of the cell to some degree, such lubricants may lead to contamination of the cell. Even with lubrication it may not be possible to crimp the cell as tightly as desired and still permit removal of the cell without damage thereto, particularly for cells with thin sidewalls, such as miniature air cells.
A prior art segmented crimping die is shown in FIGS. 8 and 9A-9C. As shown in FIGS. 9A-9C, the prior art die includes a one-piece base support 101 having a bore 102 through which a lower punch 103 may be moved. Base plate 101 is generally fixed relative to the other parts. Base plate 101 further includes a recess 104 in which a one-piece crimp die 105 is disposed. Crimp die 105 also includes a central aperture through which lower punch 103 extends. The die further includes a tapered guide housing 106 disposed in fixed relation on base plate 101 and a top plate 107 mounted atop tapered guide housing 106. Tapered guide housing 106 includes a centrally disposed tapered opening 109 for receiving four segmented dies 108a-108d. As shown in FIG. 8, which is a top view of the four segmented dies, the four segmented dies together form annular side walls of the die and define a central opening through which an upper punch 111 and a battery 110 to be crimped may be moved. Top plate 107 also includes a centrally disposed hole of the same diameter for similarly allowing upper punch 111 and cell 110 to be moved therethrough. As shown, the four segmented dies are tapered and allowed to slide vertically along the tapered surface 109 of guide 106. In this matter, as the four segmented dies 108a-108d move vertically between the upper surface of the one-piece crimp die 105 and the lower surface of top plate 107, the four segmented dies move radially inward and outward to thereby increase/decrease the diameter of the centrally disposed aperture defined by the four segmented dies 108a-108d.
In operation, the die press is positioned with the four segmented dies 108a-108d in their lowermost position resting upon the upper surface of one-piece crimp die 105. A battery 110 is placed within aperture 112, and upper punch 111 is moved vertically downward to push the cell down against the curved portion of crimp die 105. Once the cell has been crimped, upper punch 111 is raised and lower punch 103 is moved vertically upward as shown in FIG. 9B to push the crimped battery upward through aperture 112. Because of the close tolerances with aperture 112 relative to the outer dimensions of the battery, the four segmented dies 108a-108d tend to move upward as the battery is lifted by lower punch 103. As the four segmented dies 108a-108d are lifted, they will move radially outward at the same time until their upper surfaces abut the stops on top plate 107. With the four segmented dies in their uppermost position, the diameter of aperture 112 is sufficient to freely remove battery 110 from the die apparatus.
A problem exists, however, in that some of the segmented dies 108a-108d may at times become hung up, as shown in FIG. 9C. Thus, when the next battery is inserted for crimping, the battery may become misaligned and a uniform crimping of the battery may not be obtained. A similar problem can occur during crimping, with one segment rising up independent of the other segments, due to the axial component of the radial stress on the angled surface, and thereby limiting the amount of radial stress that can be applied during crimping.
Accordingly, an apparatus and method for alleviating the above-identified problems would be desirable.